The present invention relates to a catheter system for introducing and implanting a stent and comprising a catheter having at its one end an expandable portion, at its opposite end elements intended for communication with means for expanding the expandable portion, and a stent made of a material to which a permanent deformation for maintaining an enlarged transverse dimension is imparted when the catheter is expanded, said stent being arranged around the expandable portion of the catheter and releasably fixed to the catheter to prevent movement of the stent during insertion.
In case of partially occluded blood vessels, e.g. due to arteriosclerosis, it was previously necessary to perform surgery directly at the site of occlusion to cure a patient suffering from this kind of disorder. Such partial occlusion may be dilated by introducing a catheter with an expandable portion into the blood vessel and expanding the expandable catheter portion in the partially occluded area. However, this is not always sufficient since the partially occluded portion may be reestablished or relapse to its partially occluded state. In recent years it has become increasingly common to treat such cases by implantation of a stent (an endoprosthesis) into the partially occluded portion of a blood vessel. Following implantation, the stent influences the blood vessel to the effect that the latter stays dilated. In most instances, the patient will avoid more severe consequences of such disorder in the future.
Various types of catheters with expandable portions are available. A first type is designed with a portion which, under the influence of pressure, is expanded by elastic deformation of the expandable portion. This type is most often designated balloon catheters. A particular embodiment of such catheter is disclosed in UK 156674. This catheter comprises a reinforcement web in its expandable portion, said reinforcement web having a rhomb pattern. Expansion of the expandable portion of such catheter entails simultaneous reduction of the length of said portion.
A second type of catheter is made of a substantially non-elastomeric material and provided with elements which are, in the unexpanded state of the catheter, for instance rolled/folded around the remaining catheter assembly. Pressure influences will cause the expandable portions to unfold.
Stents, too, are available in various embodiments. Distinction is made between pressure-expandable stents and auto-expandable stents. The stent type relevant to the present invention is the pressure-expandable one to which pressure influences from the catheter imparts a permanent deformation until the desired introduction diameter has been reached. An example of such stent is known from EP 312852. The stent disclosed therein is a stent made from a coherent thread.
The implantation of such stent is effected by means of a catheter provided with an expandable portion onto which the stent is arranged. The catheter with the stent is introduced e.g. in the groin region if the stent is to be lodged in a blood vessel in a leg, and it is guided under x-ray monitoring to the partially occluded site whereupon means connected to the catheter applies a pressure to said catheter and the expandable catheter portion urges the stent out towards the blood vessel wall. The pressure is subsequently reduced and the catheter may then be withdrawn from the blood vessel whereas the stent in its expanded state remains in the blood vessel portion which requires treatment. The operation is relatively simple compared to the surgical intervention otherwise required at the partially occluded site and thus it is desirable in many situations.
The use of balloon catheters to deliver various types of stents has become widely used in the medical field. Such relatively non-invasive techniques offer many advantages to both patient and surgeon. Notwithstanding the advances made in this area, several problems still exist with respect to preventing the stent from unwanted movement on the uninflated balloon during insertion, placement, and final positioning of the stent prior to expansion and full deployment. Often the stent moves relative to the balloon during its negotiation through tortuous vessels and becomes off-centered on the inflatable balloon, such that it incompletely or improperly expands. In a worst case scenario, the balloon may move such that its expansion and proper positioning are not possible. For example, EP-A-0442657 discloses a catheter system of the type described above where the stent is arranged around the expandable catheter portion and where collars or sleeves are mounted on the catheter serving only to secure the stent at its end portions.
Owing to its collars, this known catheter system has a relatively large diameter. Moreover the catheter system is associated with the drawback that there is a risk of the stent moving away from the catheter surface during introduction of the catheter system through the small bending radii of a blood vessel, thereby causing damage to the blood vessel.
U.S. Pat. No. 4,950,227 discloses a similar system wherein, however, an alternative stent embodiment is used, viz. the so-called "knitted stent", whereby the risk of the stent moving away from the catheter surface is reduced but not completely eliminated. Like the above-described catheter system, however, the catheter system known from this U.S. patent is disadvantageous, too, due to the use of collars for mechanical securing of the stent and the ensuing increased outer diameter.
Efforts to solve the unwanted movement of the stent during insertion have included using adhesive to bond the stent to the balloon. For example, U.S. Pat. No. 5,100,429 employs a photo-degradable adhesive to bond the balloon to the stent. Light is then used to degrade the adhesive once the stent is inserted into the body. In this disclosure the stent used is of the type which is rolled around the catheter assembly which means that the aggregate system has a relatively large cross section at this point. Thereby the fields of application of the system are restricted. Moreover, practice has shown that there will always be residues of adhesive left on the implanted stent, which residue is to be degraded so as not to cause occlusion of the blood vessel. Thereby the implantation is rendered more difficult and the system presupposes particular adhesives, e.g. a light-degradable adhesive, and means, e.g. a light source, in connection with the catheter to degrade the adhesive.
The fact that thus the known catheter systems which incorporated stents have relatively large transverse dimensions due to their having portions which overlap the stent ends or optionally the entire stent, or due to the stent being rolled around the catheter assembly, the fields of application of such catheter systems are restricted. Moreover, there is a certain risk associated with the known systems that adhesive residues adhere to the implanted stent.
It is therefore one object of the invention to provide a catheter system of the type which in a simple manner ensures reliable securing of the stent against the catheter and simultaneously allows such catheter system to be designed with a substantially reduced transverse dimension compared to the prior art and without the risk of adhesive residues or catheter materials sticking to the implanted stent.